Analysis of stress-strain curves at fast and slow velocities of loading in vitro in the transverse section of the rat incisor periodontal ligament following the administration of beta-aminopropionitrile.

The in vitro mechanical properties of this ligament were examined by analysing the stress-strain curve obtained from a transverse section of the mandible. Mechanical measures were compared between normal rats and lathyritic rats given drinking water containing 0.2% of beta-aminopropionitrile (BAPN) for 20 days, and between the velocity of loading at 10(4) and 1 mm/24 h. The daily dose of BAPN decreased gradually because the body weight increased gradually. At the velocity of 10(4) mm/24 h, the maximum shear stress, elastic stiffness and failure strain energy density in the experimental subgroup fell to 43-50% of the control values, and at 1 mm/24 h to 71-80%. The maximum strains were not significantly different between the control and experimental subgroups either at 10(4) or at 1 mm/24 h. In the control subgroups, the maximum shear stress, elastic stiffness and failure strain energy density at 1 mm/24 h fell to 0.04-0.30% of those at 10(4) mm/24 h, and in the experimental subgroups to 0.08-0.43%. The maximum strains at 1 mm/24 h were 1.7-1.8 times greater than those at 10(4) mm/24 h in both the control and experimental subgroups. It is assumed that changes in the mechanical properties of the periodontal ligament were caused by inhibition of maturation of the periodontal collagen fibres. Assuming that the periodontal ligament is viscoelastic in nature, it is suggested that the main component reacting at 10(4) mm/24 h was an elastic one and that both components, with emphasis on the viscous one, interact at 1 mm/24 h.(ABSTRACT TRUNCATED AT 250 WORDS)